1. Field of the Invention
The present invention relates to a circuit for synchronous rectification.
2. Description of the Related Art
The use of synchronous rectification in xe2x80x98portable powerxe2x80x99 applications to reduce losses and improve efficiency is well known. A typical circuit configuration is shown in FIG. 1, where semiconductor switches 1 and 2 are both N channel power MOSFETs that are driven by a xe2x80x98dual driverxe2x80x99 3. In some configurations, power MOSFET 1 can be reversed from the configuration shown in FIG. 1, which requires some changes in the driver arrangement. Current trends in the industry are to increase the switching frequency of the apparatus to gain advantages in the reduction of magnetics and capacitor sizes, and to improve transient response.
One of the disadvantages of the current approach shown in FIG. 1 is that the reverse recovery of the diode in power MOSFET 2 (caused by the turn on of power MOSFET 1) causes switching loss every cycle and thus reduces the power handling capacity and efficiency of the circuit. The reverse recovery losses can be reduced to some extent by having an optimal deadtime in the driver between the turnoff of the power MOSFET 2 transistor channel and the turn ON of the power MOSFET 1 transistor channel. This poses practical difficulties due to the necessity of having to accommodate a wide variety of MOSFETs, layouts, temperatures and voltages.
The topology of the present invention overcomes the reverse recovery phenomenon discussed above by the fundamental means of not requiring a xe2x80x98deadtimexe2x80x99 at all and ensuring that only the channels of the transistors conduct, rather than the diodes.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.